Patent Literature 1, for example, discloses a survey system that performs photographic surveying and airborne laser scanning by using a camera and a laser emitting and receiving device which are mounted in a flying body.
In this survey system, the camera that shoots a survey target from the flying body is supported by an attitude stabilizing device called a stabilizer, and the shooting direction can be kept aligned with a vertically downward direction regardless of the attitude of the flying body in flight.
Further, the laser emitting and receiving device projects laser light to a survey target from the flying body at a predetermined period, and receives light reflected from this survey target. A control device in this survey system performs the airborne laser scanning by using information about the reflected light from the survey target which is received by the laser emitting and receiving device. The laser emitting and receiving device corresponds to a laser distance measuring device according to the present invention.
In the airborne laser scanning, both three-dimensional coordinate data about the flying body (the horizontal position and the altitude of the flying body) and information showing the attitude of the flying body in flight are needed in addition to the above-mentioned information. The three-dimensional coordinate data about the flying body, among these pieces of information, is detected by a GNSS (Global Navigation Satellite System) device mounted in the flying body. More specifically, the GNSS device receives GNSS information from a GNSS satellite at a predetermined period, and analyzes this GNSS information to acquire the three-dimensional coordinate data about the flying body.
On the other hand, the length of the period at which the laser light is projected to a survey target by the laser emitting and receiving device is shorter than the length of the period at which GNSS information is received by the GNSS device. Therefore, even if reflected light from a survey target is received by the laser emitting and receiving device, the control device cannot acquire the three-dimensional coordinate data about the flying body at a certain period not matching the period at which GNSS information is received.
In contrast with this, in conventional typical airborne laser scanning, three-dimensional coordinate data about a flying body are acquired at a certain period other than the period at which GNSS information is received, by using information about acceleration along three axes and angular acceleration along three axes which are measured by an IMU (Inertial Measurement Unit) mounted in the flying body.
However, because the IMU is very expensive and is relatively heavy, a limitation is imposed on the types of flying bodies into which this IMU can be incorporated.
Accordingly, in the survey system described in Patent Literature 1, instead of the IMU, an accelerometer and an angular accelerometer which are less expensive and smaller than the IMU are disposed.
More specifically, this survey system acquires three-dimensional coordinate data about a flying body at a certain period not matching the period at which GNSS information is received, by using both information about acceleration along three axes from the accelerometer and information about angular acceleration along three axes from the angular accelerometer.
Further, information showing the attitude of the flying body is angles in a rolling direction, a pitching direction and a yawing direction of the flying body (referred to as a roll angle, a pitch angle and a yaw angle from here on), and values acquired by bundle calculation for corresponding points of images which are shot from two or more different positions by a camera are used. The control device calculates an attitude of the flying body at each scan period of laser light (this period does not match the period at which the GNSS information is received) in accordance with the attitude of the flying body acquired by the bundle calculation and by using both the acceleration from the accelerometer and the angular acceleration from the angular accelerometer.